1. Field of the Invention
The invention relates to a method for measuring the thickness of objects by diffracting a coherent beam of light through an aperture or across an edge and comparing the diffraction pattern to a reference diffraction pattern.
2. Related Art
In the manufacturing environment, there is often a need to measure the thickness of manufactured components or workparts with a high degree of accuracy. In some applications, thickness measurements with micron or submicron resolution are necessary.
In situations requiring high resolution thickness measurements, it has been proposed to use the technique of laser triangulation, in which measurements are calculated based on the reflection of multiple laser beams off the surface. One problem with optical measurement methods results from the so-called “noise” created by unwanted light reflections. Such noise can produce false positive and/or false negative measurements. In high-volume mass production manufacturing operations, quality control standards often require defective parts statistics less than one or two parts per million. When the difference between an acceptable and unacceptable workpart is a thickness measurement in the range of a few microns, achieving and maintaining consistent production quality can be a challenge.
Accordingly, there is a need for a thickness measuring technique which is highly accurate, robust, not sensitive to light noise created from unwanted reflections, and adaptable to high production volume settings.